Crystallization of ddt



Patented Nov. 2, 1948 CRYSTALLIZATION F DDT Kenneth B. Little and JohnJ. Burton, Easton, Pa., assignors to J. T. Baker Chemical 00.,Phillipsbnrg, N. J a corporation of New Jersey No Drawing. ApplicationJune 25, 1947, Serial No. 757,052

2 Claims. (Cl. 260649) This invention relates to improvements in themanufacture of technical or commercial dichlorodiphenyl trichloroethane,the insecticidal material designated as DDT.

Technical DDT is a solid material at ordinary temperatures, but readilymelts at below 100 C., usually at about 90 C. Pure DDT melts at about106 C. or somewhat higher.

In the usual process of manufacture, it is first obtained in moltenform, the molten material is allowed to cool and solidify, and the solidproduct so obtained is ground for use as a powder. When DDT issolidified by this procedure, the solid material obtained is somewhatgummy due to incomplete crystallization. It is, therefore, commonpractice to age it for substantial periods of time, for example 16 to 40hours, before grinding.

In some cases, the molten material is solidified on a cooled, rotatingdrum and produced as flakes of the solid product. Where the product issolidifled on a flaking drum, the drum must be rotated very slowly, thusrequiring a large capital investment in the solidifying equipment for agiven production.

With the foregoing procedures, there is a definite tendency for theproduction of a material with segregated isomers or crystals, which isundesirable.

The present invention provides improvements in the conversion of themolten DDT to the solid form which gives a product which is free fromgummy characteristics, which'has no segregation of isomers or crystals,which is more easily ground than the previous products, is more brittleand is somewhat different in appearance, having a chalky whiteappearance. It may be ground without aging, and the storage binsrequired for such aging are thus unnecessary. Furthermore, the inventionpermits the production of the solid ma terial at a substantially higherrate from given equipment than has heretofore been possible.

In accordance with the present invention, the molten DDTis supercooledbelow its normal crystallization temperature and after suchsupercooling, it is permitted to solidify without further cooling.Advantageously,the supercooling is such that the temperature of thematerial, before crystallization begins, is between 45 and 60 C. but itmay be below 45, or somewhat above 60 C. It is important, in order thatsupercooling may be obtained, to cool the material quickly and with aslittle agitation as possible and also to avoid or minimize contact ofthe material with solidified DDT.

The procedure may be carried out in various ways, as by the use of filmtype shell and tube heat a body of the molten DDT and. have the filmscraped off after cooling but prior to solidification, or in other formsof apparatus.

Advantageously, a conventional flaking machine, operated with rapidrotation of the drum so that supercooled liquid rather than a solidifiedproduct is produced, is used. The important factor in carrying out theprocess is the cooling at a rate sufficient to produce a supercooledliquid, such cooling being from the temperature of the molten DDT, sayaround 100 C., to a temperature below its normal solidification point,advantageousiy from about to about C., at a rate.

suificient to avoid crystallization during the cooling operation. Thesupercooled liquid then is allowed to stand with resultantsolidification to form the easily ground product of the invention.

- The invention will be illustrated by the following examples but it isnot limited thereto.

Example I.- grams of DDT (technical) were melted and heated to 100 C.and poured into a prewarmed porcelain dish. It was then allowed to coolto 55 C. without agitation, by exposure to room atmosphere. At this timethe liquid was stirred vigorously, whereupon it crystallized into ahard, brittle, uniform mass, the solidification being accomplished by arise in temperature to about 64 C.

Example II.DDT at 100 C. was fed to the inside surface of a verticaljacketed stainless: steel pipe, inside diameter and4' long, used as afilm type cooler. The rate of feed was 147 grams per minute. Coolingwater was circulated through the jacket. The DDT was discharged at 53 to59 C., and was then placed in a container and allowed to cool. Itcrystallized without stirring to a hard, brittle, uniform. mass freefrom the gummy characteristics of DDT as ordinarily crystallized, and ofa nature such as to permit ready grinding.

Example III.DDT at a temperature of 100 I 3 at the rate of 8 revolutionsper minute. The product was discharged at the rate of .84 lb. per minuteat 50 to 52 C. and delivered to a container where it cooled to roomtemperature and crystallized into a hard, brittle, uniform mass.

The apparatus in accordance with Example III is, of course, of the typeof conventional flaking machines. The important distinction in operationas compared with flaking machines herelofore used for the solidificationof DDT is the rapid rate of rotation of the drum with the prodnet of asupercooled liquid, as distinguished from a flaked solid.

Example IV.-Mo1ten DDT at 100 to 102 C.

was cooled as in Example III with the super- 4 We claim: 1. The processoi. solidifying DDT (dichiorodiphenyl trichloroethane) in hardcrystalline form which includes cooling molten DDT to a temperature notabove about 60 C. without so1idi-' flcation, whereby a supercooledliquid is obtained, and permitting the supercooled liquid tocrystallize.

2. The process as in claim 1 where the supercooling is carried out bytransferring heat from .a film of the molten DDT to a cooled surface.

' KENNE'IH B. LITTLE.

JOHN J. BURTON.

- REFERENCES CITED The following references are of record in the flle ofthis patent:

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